Sorry. Another NMEA question.

[Bav34]

Further to yesterdays post I have now connected the relevant NMEA wires from my GPS to my wind speed .... and nothing happened.

Going through the techie bits in the two handbooks I have found the following:

Windspeed:

Interfaces:

NMEA 0183 outputs MWV,VPW
NMEA 0183 inputs RMC,VHW,VTG .

The GPS has a screen that lists 20 OUTPUTS including GPRMC , GPVTG and SDVHW.

There is an option to put a tick alongside each. There is NO input screen despite there being an input wire as per yesterdays query.

Do I need to select ALL three ''output sentences'' or ......what????

Thanks again.

Steve

 

[wooslehunter]

Depends on what you want to do & what your equipment is capable of. I assume you just want to make sure the wind instrument can display true and apparent. It wind instrument can only measure apparent on its own. To show true speed and direction, it needs to know the speed it is moving at. This is the speed over the ground, SOG and not through the water. If there's any tide they will be different.

VHW = water speed & heading. A log may output this.
RMC = Recommend Minimum Specific GPS/TRANSIT Data (actually contains position, speed (SOG) & course)
VTG = track made good & ground speed (SOG).

All of the NMEA input sentences contain speed. However, water speed takes no account of tide and will only be valid if you have a log connected to the GPS. If you're doing 1kt into a 1kt tide, water speed will be 1kt but speed over the ground, SOG, will be zero. VHW is water speed only but would be output directly from a log.

Use RMC or VTG. They both contain SOG.

The NMEA output will send information back to other systems.

MWV = wind speed and angle
VPW = speed measured parallel to the wind